Ok I swear I'm not trying to advertise anything and I haven't been physed. I really love Portal, and i was kinda bummed that I bought it on xbox360 because they have new content that you can only use on your computer. major bummer I know.
Cutting to the chase:
between now and may 24th (I believe) you get portal complimentary when you install steam (steam is free)
Basically they want you to download steam so they can advertise to you, but who cares!
PORTAL IS FREEEE!!
Ok I love the game and if I find any strings at all I'll report them I promise
Link to steam website (hope that's not taboo listing a link) (I guess I'll hide it so nobody sees it
(SPOILER)http://store.steampowered.com/